Means for reproducing position



Ap 1929 E. M. HEWLETT ET AL 1,708,884

MEANS FOR REPRODUCING POSITION Filed April 22. 1925 Fi .Z. 6 2

\ Inventor-s: Edward M.He wle-tt,

Waldo W.W\Har d,

Their A-ttorneQ.

Patented Apr. 9, 1929,

UNITED STATES PATENT o icE.

EnwAan'n: nnwLE'r'r AND WALDO w. WILLARD, or SGHENEGTADY, NEW YORK, AS-

sronons r QENEBAL ELECTRIC comrm, A conroaa'rron or NEW roan.

MEANS FOR nnraonuome 'IOSITION.

uses. flledApril 22,

This invention relates to means for re-- producing position and has forits object the'provision of improved means for m ain taimng one objectin positional agreement with a second object constituting a control lingobject.

meansfo-r driving an object intopositional agreement with a remotelysituated controlling object of the type in which 'the'driving object isactuated by an electric motor wh ch is.'controlled by the controllingobject through the agency of one or more receivers of the movement's ofthe controlling object. A system of this character is described andclaimed, for example, in a patent to Edwin J. Murphy and Leonard P.Hutt, No. 1,559,525 of Oct. 27, 1925, and assigned to the same assigneeas this invention. Our inven tion is particularly useful in-reproducingat a distance the position of an object having angular motion, such as atelescope. Where the motion, of the controlling object is transmitted bymeans of low speed and high speed systems, this motion being reproducedby low speed and high speed receivers, it is important for-successfuloperation of the system that the low speed receiver retain control ofthe servo motor until the control mechanism operated by the high, speedreceiver has turned to such a position that it may take over thecontrol. In the aforesaid copending application contact arms areconnected to the receivers through 5 heart-cam couplings by means ofwhich the contact is reversed each half revolution. With this controlmechanism the contact arm must be turned to some point within thecorrect revolution with relation to the high speed receiver in orderthat the high speed receiver can properly control the motor.- If thiscondition does not exist the high speed receiver will cause the motor'torun to a wrong position. 1

Where the driving means for the transm'mter of the low speed receiverhas an appreeiable error, it may happen that the control will be givenover to the high speed receiver toosoon, due to the effect of this trolto some point within'2 fromits acmeans for prolonging the control by thelow error. This is especially true where the 1925. serial no. 25,112.

connection of the transmitter of the low fspeed receiver, the low speedreceiver must More specifically this invention relates to retain controlto a point which is 2 minus the :amount of error from its true positionn order that the high speed receiver may be 1n position to take u thecontrol. Under these conditions, if t e low speed receiver gives upcontrol at the 2%? point, then the high speed receiver will not operatethe motor correctly.

- In carrying outour invention we provide speed receiver in such'mannerthat the low speed receiver must-turn very near its accurate positionbefore the control is turned over to the high speed receiver.

\ For a more complete understanding of our invention, reference shouldbe had to the accompanying drawing in which Fig. 1 is an end elevationview of a control device embodying our invention; Fig. 2 is a sideelevation view of Fig. 1; while Fig; 3 is a view showing in diagrammaticfashion a system for reproducing position involving our lnvention.

Referring to Fig. 3 of the drawing, we have shown. our invention in oneform as applied to a 'system for driving an indicating dial 10 inaccordance with the movements in a substantially horizontal plane of aremotely situated telescope 11. The dial 10 is turned by means of anelectric servo motor 12, the shaft 13 of which is geared to the dialthrough a worm gear connection 14. The servo motor 12 is controlled bymeans of two receivers or'reproducers of angular motion 15 and 16, whichare electrically connected respectively to transmitters 17- and 18operated by the telescope. As shown, the transmitter 17 is connected tothe telescope through a suitable gear train 19 1 to operate at asuitable high speed ratio such as 72: 1 with the movement of thetelescope, while the transmitter 18 is driven in a 1: 1 ratio with thetelescope.

.The receiving and transmitting instru- 5 ments 15 to 18 inclusive maybeof any suitable type. Preferably an alternating current type is used,each instrument being provided with a polycircuit, armature winding anda field. winding. As shown, the transmitters 17 and 18 are provided withfield windings 20 and 21 on their rotor members and with deltaconnected, bi-polar, three phase armature windings 22 and 23 on theirstator members. The receivers 15 and 16 are similar in construction tothe transmitter. Like points of the armature windings of the receiver 15and the transmitter 17 are connected by means of three conductors 24,and in similar manner like points of the armature windings of thereceiver 16 and the transmitter 18 are connected by three conductors 25.The field windings of all four devices are connected to a single phasealternating current supply source 26.

In the operation of systems of this character for transmitting angularmotion, electromotive forces are induced in the armature windings of thetransmitting and receiving devices by the cooperating field windings.These voltages result in an exchange of current between the armaturewindings whereby the rotor of the receiver is turned to a positioncorresponding to the position of the transmitter in which position thevoltages in the two armature windings are equal and opposite. Anymovement applied to the transmitter results in an. unbalanced voltagecondition whereby the receiver is caused to follow. It is acharacteristic of instruments of this type that if the receiver lagsmore than 180 behind its transmitter, its torque will be reversed and bein a direction to cause it to turn into angular agreement by completinga whole revolution of lag.

The stator members 15 and 16 of the receivers 15 and 16 are rotatablymounted and are connected to the servo motor 12, the stator 15 havingsecured to it a gear 27 which meshes with a gear 28 on the shaft 13 ofthe motor, while the stator 16 is connected to the shaft 13 through areducing gear train 29. The driving ratios of these connections betweenthe stators and the shaft 13 are such that the stators are driven in a72 :1 ratio, the stator 15* having the higher speed.

The rotors 15 and 16 of the receivers have their shafts 30 and 31connected to contact devices 32 and 33 respectively, whereby thestarting, stopping and direction of To tation of the servo motor iscontrolled in accordance with the movement of the receivers. The contactdevices are connected to the receiver shafts through yieldable couplingscomprising heart shaped cams 34 and 34*,

with which cooperate spring pressed rollers 35 and 35 respectively,whereby the receivers are free to turn around immediately, under thesmall restraint offered by the couplings, to their proper positionsindependently of the contact devices. The contact de vices operated bythe receivers 15 and 16 are somewhat similar in construction and conse-1,7os,sse

quently only one will be described in detail, i. e., the device drivenby the low speed receiver 16.

Referring to Figs. 1 and 2, a frame or support 36 is secured to the endof the rotor shaft 31 of the low speed receiver. The heart shaped cam 34is rotatably mounted in this frame 36 'on a shaft 34 which is mounted inbearings 37 and 38 so that its axis of rotation is coincident with theaxis of shaft 31. The roller 35 is carried on the end of an arm 39,which is pivotally mounted on the frame 36. Bearing against the arm 39is a helical spring 40 which forces the arm toward the heart-cam andthereby maintains the roller in engagement with the cam. The heart-camis constructed and arranged on its shaft 34 in such manner that theroller 35 is caused by the spring 40 to seek a posi tion of rest at thebase of the cam, as shown in Fig. 3.

The outer end of the cam shaft 34 projects beyond the frame 36, and hassecured to it a contact arm 41. This contact arm is provided with twobranches 42 and 43 on its upper end extending in directions to form anacute angle with each other. On opposite sides of the contact arm aresecured resilient contact members 44 and 45, made of a suitable magneticmaterial, such as steel. These members are secured to the contact arm attheir lower ends only, for example, by means of bolts 46 and 47, and areprovided on their upper ends with contacts 48 and 49. Upper portions 44and of the contact members are bent outwardly in parallelism with thebranches 42 and 43. The upper ends of the members 44 and 45 terminatesubstantial distances below the ends of the branches 42 and 43, andextend under stops 50 and 51 carried by the branches.

As shown, these stops consist of headed members which are threaded andscrewed into tapped bores in the branches 42 and 43; As shown, the upperends of the branches 42 and 43 may be bifurcated to form two resilientprongs which are sprung together slightly so that the stops when screwedinto them are secured in any adjusted position. The upper'ends of themembers 44 and 45 project under the heads of the stops 50 and 51, which,therefore, limit the outward movement of the members with relation tothe contact arm.

The lower end of the contact arm is provided with a weight 52, and isalso bifurcated so that the two portions thereby formed may be drawntogether by means of a screw 53, and the contact arm thereby clampedsecurely on the shaft 34 of the heart-cam.

Closely adjacent the contact arm on opposite sides thereof are twostationary contact members 54 and 55, the upper ends of which extendsubstantially parallel with the are of reduced size and extend throughelec-.

trically insulating bushings 56 and 57*. As shown, the larger outer endsof the screws are threaded and secured in tapped holes in blocks 56 and57 made of a suitable electrically conducting material such as brass,

and these blocks 56 and 57 are secured in turn to insulating plates 58and 59 which are mounted on the upper ends of the members 54 and 55, thevarious mechanical connections being made by suitable screws. The plates58 and 59 may be made of. any suitable electrically insulating material,such as bakelite. The screws 60 and 61 securing the blocks 56 and 57"vrespectively to the plates 58 and 59 are also utilized as binding postsfor making electrical connections with the contact screws 56 and 57.

- Magnet coils 62 and 63are secured 'to the upper ends of the members'54 and 55 respectively. These magnet coils are provided with cores ofsuitable material, such as iron. The cores consist of plates 64 and 65secured to the members 54 and 55 and having their inner ends bent overto provide pole faces 64' and 65 adjacent and opposite the mem bers 44and 45 respectively. The outer ends of the plates 64 and 65 terminate atthe sides of the coils respectively, and carry core members 64 and 65which extend through the coils. The remaining portions of the cores forthe coils are formed ,by screws 66 and 67 which extend through themembers 64 and 65? and terminate adjacent the members 44 and 45respectively, thus forming the opposite poles of the electromagnets. Thescrews 66 and 67 are mounted in tapped holes in the members 54 and 55and can be adjusted as desired. One terminal of the coil 62 is connectedto the contact screw 56 by means of the the screw60, and one terminal ofthe coil 63 is connected to contact 'not the equivalents of theelectromagnets of the device 33.

Referring now to Fig. 3, the servo motor 12 is shown as a shunt typemotor having its field winding 70 permanently connected throughconductors 71 and 72 to the supply mains 73 and 74 leading to a suitabledirect current supply source. The armature winding of the motor isconnected to the supply mains 73 and 74 through conductors 75 and '76anda relay switch 77 comprising two pivoted contact arms 78 and 79 whichare normally forced apart by an insulated spring 80 into engagement withthefixed eontacts 81 and 82 respectively, as shown in the drawing. \Vhenthe'contact arms are 1n these positions, the armature is short circuitedthrough a conductor 83 connecting the contacts 81 and 82 to gether, andalso connectinm them to the supply main 74. 'Between the contact arms isa stationary contact 84 which is electrically connected to the supplymain 73. By

moving the contact arm 78 into engagement.

with contact 84, the armature of the motor 12 is connected across thesupply means 73 and 74 for operation in one direction, while by movingthe contact arm 79 into engagement with contact 84 the armature isconnected across the supply mains with the opposite polarity foroperation in the opposite direction. Insulated stops 85 and 86 areprovided on the contact arms respectively, and are arranged to engage.with each other when one of the contact arms is in engagement withcontact '84 and thereby insure that when one of the contact arms is inengagement with contact 84 the other shall remain in contact with 81 or82, as appropriate.

The contact arms 78 and 79 by magnet coils '87 and 88 respectively. Oneterminal of each of the coils is connected through a conductor 89 to thesupply main 74. The remaining terminal of the coil 87 is connected bymeans of conductors 90 and 91 through the magnet coil 63 to the areoperated I stationary contact screw 57, and also by means of aconductor92 leading from conductor 91 to the contact screw 57 of the contactdevice 32. The remaining terminal of the coil 88 is connected by meansof conductors 93 and 94 through the magnet coil 62 to the contact screw56, and also by means of a conductor 95 connecting with the conductor 93to the contact screw 56 of the contact device 32. It will be understoodthat the contact screws 56 and 57* associated with the contact device 32correspond respectively with the contact screws 56 and 57 associatedwith the contact device 33. The contact arm 41 is connected by means ofa conductor 96 through a magnet coil 97 to the supply main 73, while thecorresponding contact arm 41 of device 32 is connected through aconductor 98 and a resistance 99 to the supply main 73.

The magnet coil 97 operates a switch 100 and when energized closes theswitch 100, thereby short circuiting 'a resistance 101 which isconnected in the circuit between the stationary contacts 81 and 82. andthe supply main 74. The resistance 99 is substantially of the same valueas the resistance of the magnet coil 97. It is provided to prevent shortcircuiting and consequent deenergization of the coil 97 in case the twoare connected in parallel through the contact devices.

In the operation of the system it will be understood that when thetelescope is moved to a new bearing the rotors of the receiversreproduce this movement in their respective ratios whereby the contactarms 41 and 41 are actuated. Assume, for example, that the telescope isrotated rapidly through a considerable angle in such direction that thecontact arm 41 is thrown into engagement with contact 56, the contactarm 41 being thrown into engagement with contact 56. A control circuitis thereby closed from the supply main 74 through conductor 89, themagnet coil 88, conductors 93 and 94, contact arm 41, conductor 96 andcoil 97 to the supply main 73. This energizes coil 88 which throws thecontact arm 79 into engagement with the stationary contact 84 whereby acircuit is closed for the armature of the servo motor 12 from supplymain 74 through contact arm 78, conductor 75, the armature, conductor76, and contact arm 79 to the supply main 73. The servo motor is thuscaused to rotate in a direction to cause the dial 10 to follow thetelescope. By reason of the fact that coil 97 is energized, theresistance 101 is short circuited during the operation of the motorunder the control of contact arm 41, and the motor consequently operatesat high speed. The motor 12 at the same time drives the stators 15 and16 in directions opposite to the movements of their rotors whereby therotors are carried back toward their original angular positions.

As the motor continues to rotate the dial I and the stators, it will beobserved that the rollers 35 and 35 will gradually move back.

toward their seats at the bases of the heartcams and finally, when thedial 10 has been driven into angular agreement with the telescope withinthe limit of the accuracy of the low speed receiver 16, contact arm 41will be moved to disengage contact 56, thus transferring the control tothe high speed receiver for the accurate adjustment of the dial. Thecontact arm 41 will then be in engagement with contact 56 whereby acircuit is maintained for the coil 88, this circuit being from supplymain 74 through conductor 89, the coil 88, conductors 93 and 95, contactarm 41, conductor 98 and resistance 99 to the supply main 73. The motorcircuit is thus maintained and the motor continues the adjustment of thedial, the circuit of coil the circuit of the coil 88 is broken thecontact arm 79 is thrown into engagement with contact 82 by the spring80 toshort circuit the armature of the motor and bring it torest quicklybydynamic braking.

It will be observed that when the high speed receiver 15 has control,the coil 97 is not energized and the resistance 101 is, therefore,included in the armature circuit of the motor and consequently the motoroperates at a slower speed, and can, therefore, be stopped much quickerthan would be possible when operating at high speed under the control ofthe low speed receiver. This facilitates the stopping of the dial inaccurate angular agreement with the telescope.

When the telescope is moved in the opposite direction the contact arms41 and 41 are also moved in the opposite direction whereby the armaturecircuit is closed in the reverse direction, the low speed receivermaking the coarse adjustment of the dial and the high speed receivermaking the accurate adjustment substantially as previously described. Inthis case, the contact arm 41 engages the contact 57, thereby closmg acircuit from supply main 74 through conductor 89, coil 87, conductors90- and 91, contact arm 41 and coil 97 to the supply main 73. Upon thecompletion of the coarse adjustment the control is taken over as beforeby the. high speed receiver, contact arm 41 then being in engagementwith con tact 57, whereby a circuit is closed from the supply main 74through conductor 89, coil 87, conductors 90 and 92, contact arm 41,conductor 98 and resistance 99 back to the supply main 73.

The heart-cam couplings between the contact arms 41 and 41 and theirrespective receivers permit the receivers to turn at once to positionsof angular agreement with their transmitters, as previously noted, Thisfeature is of particular importance where the receivers are switched onthe transmit. .ters with the dial considerably out of angular agreementwith the telescope. If a rigid connection were provided, so that thereceivers would be prevented from snapping at once into angularargeement with their transmitters, excessive current flow and consequentoverheating of the transmitting and receiving instruments would result,and furthermore the accuracy of other receiving instruments which mightbe operating on the same circuit would be seriously affected.

Another function of the heart-cam coupling is to cause the dial to bedriven through the shortest angle into positional agreement.

For example, in case the dial should lag more than 180, for any reasonwhatever, as might occur if the telescope were swung around with greatrapidity, it will be observed that the roller 35 connected to the lowspeed receiver will pass over the point of its heart-cam 34, thusreversing the armature circuit of the motor and causing it to reverseand drive the dial in the opposite direction into angular agreement bycompleting a revolution of lag.

\Vhen the low speed. receiver has control, the rotor of the high speedreceiver may and probably will be turned with its stator by the motorthrough a number of complete revolutions, the roller 35 then moving overits heart-cam 34. When this takes place it will be observed that thecontact arm 41 will be reversed each half revolution of the receiver 15due to the effect of the heartcam, but this has no effect on theoperation of the motor since the stops 85 and 86 prevent the operationof both of the contact arms 7 8 and 7 9 at the same time, andconsequently prevent the high speed receiver from taking control as longas the low speed receiver has control.

Ordinarily during the usually relatively slow training of the telescope,the dial is caused tofollow the telescope under the control of the highspeed receiver only, and it is only when switching or high speedtraining is done that the low speed receiver is called upon to takecontrol. The adjustment of the contact devices 32 and 33 is such thatjust before the lag of the dial is suflicient to cause the roller 35 tomove over the point of the heart-cam 34 the contact arm 41 will makecontact so that should the roller 35 move over the point of the heartcam34 and reverse the contact arm 41, the motor circuit will be maintainedin the proper direction by the contact arm 41.

It will be observed that due to the reversing effect of the heart-camcoupling each helf revolution, the low speed receiver must adjust thedial with suflicient accuracy to bring the roller 35 onto the correctrevolution of the heart-cam 34, i. e., within 180 of its correctposition on the heart-cam, before the high speed receiver takes control.If this condition is not established when the high speed receiver takescontrol, the motor will be reversed and the dial driven in the wrongdirection. With the 72:1 speed ratio for the high speed receiverpreviously assumed, this means that the low speed receiver must maintaincontrol until the dial has been moved to some point less than 2 from itsaccurate position. No difliculties would be encountered in making thevproper adjustments of the contact devices 32 and 33 to bring this about,provided there are no inaccuracies in the various driving connectionsfor the transmitting and receiving devices. Ordinarily, suchinaccuracies are due to inaccuracies in manufacture, wean-etc. Thedriving connection between the telescope and the transmitter 18 may havean appreciable error, and ordinarily the driving gear train between themotorand the stator 16 of the low speed receiver will have anappreciable error. Such errors, particularly in gear trains, arecumulative in some positions and subtractive in other positions, andconsequently the controlmechanism must be adjusted accordingly.

Let it be assumed that the inaccuracy in the driving connections of thelow speed receiver amounts to 1 4. When this error is cumulative, thelow speed receiver must take the control at a point somewhat less than 2f minus 1 A or 1% from the accurate position of the dial in order thatthe high speed receiver may operate properly, but when this error issubtractive the low speed receiver must take control at a point greaterthan 1 from the accurate position of the dial, else it may take controland operate the dial due to error displacement. It is obvious from thisthat with an error ofl fl which may be either cumulative or subtractive,it would be impossible to correctly adjust the contact mechanism of thelow speed receiver as long as the control is given up at approximatelythe same point as it is taken over. It is the function of the electromagnets 62 and 63 to permit such an adjustment, whereby the control, oncetaken at the proper point, will be retained until the dial is very closeto its accurate osition.

' It will be observe that since the magnet coils 62 and 63 are connectedin the control circuits they are not energized until their particularcontrol circuit is closed by the contact arm, and consequently theelectromagnets do not exert an attractive force on the arms 44 and 45 beore contact is actu' ally made. Thus, when the contact arm engages thecontact 56 the magnet coil 62 is energized and maintains the contacts inengagement until they are positively separated by the engagement of stop50 with the end of member 44. The separation of the contacts, however,opens the circuit of the magnet coil 62 whereby the member 44 isreleased. The effect of magnet coil 63 on member 45 is similar. Wherethe error is plus or minus 1 4 in the driving connections, theadjustment of the contacts'56 and 57 would be such that contact would bemade when the dial is somewhatmore than 1 A but less than 2 from itsaccurate position, and the adjustment ,of the screws 66 and 67 and thestops 50 and 51 would be such that the contact once made would not bebroken until the dial hadbeen turned to a position less than 1%" fromits accurate position.

"While wdhavedescribed our invention as 1 said objects whereby saidmotor is caused to I What we claim as new and desire to secure byLetters Patent of the United States is 1. Means for reproducin prisingin combination wit movable object and a driven movable ob ect, a motorfor driving said driven object, control means for said motor actuated inaccordance with the movements of said objects arranged to operate saidmotor upon the occurrence of apredetermined positional disagreementbetween said objects, and auxillary means responsive to a condition ofoperation of said motor for maintaining said motor in operation untilsaid driven object has been moved to a predetermined relative positionin'which the positional disagreement between said objects is lessv thanthat required to start said motor. I

2. Means for reproducin position comprising in combination wit 1 acontrolling movable object and a driven movable object, an electricmotor for driving said driven object, control meansfor said motor,operating connections between said control means and drive said drivenobject into positional agreement with said controlling object, andauxiliary means responsive to a condition of operation of said motorassociated with said control means for maintaining said control means inclosed circuit position until said driven object has been moved to apredetermined position after said control means would otherwise bein'open circuit position.

3. Means for reproducing position comprising in combination with acontrolling a movable object and a driven movable object,

an electric motor for drivin said driven object, means operated by saldcontrolling object for closing the circuit of said motor upon apredetermined angular disagreement between said objects whereby saidmotor is caused to drive the driven object into angu- .lar agreementwith said controlling object,

holding means responsive to the closing of said motor circuit formaintaining said circuit closed as said driven object is moved towardangular agreement with said controlling object, and means operated bysaid controlling object for opening said motor circuit when said-drivenobject has assumed a predetermined position with relation to saidcontrolling object, whereby said holding I means is renderedinefl'ective.

4. Means for reproducing position comprising in combination with acontrolling movable object. and a driven movable object, an electricmotor for driving said driven obv ject, means operated by saidcontrolling position coma controlling controlling object for openingsaid circuit when said driven object has assumed a predetermined ositionwith relation to said controlling o ject.

5. Means for reproducing position comprising in combination with acontrolling movable object and a driven movable object, an electricmotor vfor driving said driven object, a pair of spaced contacts, acontact arm movable between said contacts to control the circuit of saidmotor for either direction of rotation, driving connections between saidcontact arm and said objects whereby said contact'arm is moved to engageone of said contacts to start said motor upon movement of saidcontrolling object and moved toward an intermediate position betweensaid contacts in response to movement of said driven object so that saidmotor is caused to drive said driven object into positional agreementwith said controlling object, and means responsive to a condition ofthe'motor circuit whereby contact once established is maintained untilsaid contact arm has been moved toward an intermediate position betweensaid contacts a predetermined distance from the position in whichcontact was established.

6. Means for reproducing position comprising in combination with acontrolling movable object and a driven movable object, an electricmotor for driving saiddriven obj ect, a control device for said motoroperated in accordance with the movements of said objects provided witha resilient contact member, a magnet'coil energized upon the closing ofa circuit by said contact member arranged to exert an attractive forceon said contact member to maintain said circuit closed, and means formoving said contact member against the pull of said magnet coil to openthe circuit of said motor.

7. Means for reproducing position comcontact members carried by said armarranged to engage said contacts to control the circuit of said-motorfor either direction "of rotation, magnet coils in the circuits withsaid contacts, each coil being arranged to exert an attractive force onone of said resilient contact members when its circuit is closed by saidresilient member and thereby maintain said motor circuit closed whensaid arm is moved toward an intermediate position-between said contacts,and stops carried by said arm arranged to move said resilient membersagainst the pull of said magnet coils to open the circuit therethrough.

8. Means for reproducing position comprising in combination with acontrolling movable object and a driven movable object, an electricmotor for driving said driven object, a fixed contact, a resilientcontact member made of magnetic material operated by said controllingobject arranged to close a control circuit for said motor when movedinto engagement with said fixed contact upon movement of saidcontrolling object, a magnet coil in said control circuit arranged toexert an attractive force on said contact member to maintain saidcircuit closed, and means operated by said driven object cooperatingwith said contact member to open said circuit against the pull of saidmagnet coil when said driven object .has assumed a predeterminedposition'with relation to said controlling object. a

9. Means for reproducing position comprising in combination With acontrolling movable object and a driven movable object, an electricmotor for actuating said driven object, a pair of spaced fixed contacts,an arm actuated in accordance with the movements of said obj ects, apair of resilient contact members made of magnetic material on said armmovable by said controlling object into engagement with one or the otherof said fixed contacts to close control circuits for said motor for bothdirections of rotation, magnet coils adjacent said fixed contactsconnected in said control circuits arranged to exert an attractive forceon their respective contact members when energized by the closingof acontrol circuit thereby and maintain said circuit closed when said armis turned toward an intermediate position between said fixed contacts assaid driven object is moved toward positional agreement with saidcontrolling object, and means carried by said arm for engaging saidresilient members to open the control circuit when said driven objecthas assumed a predetermined position with relation to said controllingobject.

10. Means for reproducing position com-' prising in combination with acontrolling movable object and a driven movable object, a motor fordriving said driven object, control means for said motor, low and highspeed receivers of angular motion responsive to the movements of saidcontrolling object, operating connections between said receivers andsaid control means whereby said motor is operated under the control ofsaid low speed receiver for a coarse adjust- -ment and under the controlof said high speed receiver for a fine adjustment so as to drive saiddriven object into positional agreement with said controlling object,said control means being arranged to operate 'said motor under thecontrol of said low speed receiver upon the occurrence of apredetermined positional disagreement between said objects, andauxiliary means responslve to a condition of the motor circuit forcausing said low speed receiver to retain control until said drivenobject has been moved to a predetermined relative position in which thepositional disagreement between said ob ects is less than that requiredto caulse sa d low speed receiver to take contro 11. Means forreproducing position comprising in combination with a controllingpositional agreement with said controlling object, said control meansbeing arranged to operate said motor under the control of said low speedreceiver upon the occurrence of a predetermined positional disagreementbetween said objects, holding means responsive to the control of saidmotor by said low speed receiver causing said low speed receiver toretain control until said objects are in closer positional agreementthan when said motor was started, and means for transferring the controlof said motor to said high speed receiver when said driven object hasassumed a predetermined position with relation to said controllingobject, whereby said holding means is rendered ineffective.

12. Means for reproducing position comprising in combination with acontrolling movable object and a driven movable object an electric motorfor driving said driven object, low and high speed receivers of angularmotion responsive to the movements of said controlling object, controlmeans perated by said receivers and by said driven object for openingand closing control circuits for said motor so that said motor isoperated under the control of said low speed receiver for a coarseadjustment and under the control of said high speed receiver for a fineadjustment and thereby caused to drive said driven object intopositional agreement with said controlling object,-

means responsive to the closing of a control circuit by said low speedreceiver for maintaming said circuit closed, and means for was started,whereby the control of said motor is turned over to said high speedreceiver.

13. Means for reproducing position comprising in combination with acontrolling movable object and a driven movable object, an electricmotor for driving said driven object, low and high speed receivers ofangular motion responsive to the movements of said controlling object,control devices for said motor operated by said receivers respectively,a resilient contact member for the control device operated by said lowspeed receiver, a magnet coil energized on the closing of a circuit bysaid contact member arranged to exert an attractive force on saidcontact member to maintain said circuit closed, and means for movingsaid contact member against the pull of said magnet coil to open saidcircuit, whereby the control of said motor is turned over to said highspeed receiver.

14. Means for reproducing position comprising in combination with acontrolling movable object and a driven movable object,

an electric motor for driving said driven ob-.

ject, low and high speed receivers of angular motion responsive to themovements of said controlling ob ect,-said receivers having theirstators rotatably mounted, arms movable by said receivers respectivelybetween pairs of spaced contacts to start said motor, drivingconnections between said motor and said stators arranged to turn saidreceivers in directions opposite to the movements of their rotors andthereby move said arms toward intermediate positions between said pairsof spaced contacts to stop said motor, resilient cont-act memberscarried by the arm operated b said low speed receiver, and magnet coilsin the circuits with said contact members, each coil being arranged toexert an attractive force on one of said contact members when itscircuit is closed and thereby cause the low speed receiver to retaincontrol of said motor when said low speed receiver. arm is moved towardan intermediate position between said contacts, and stops carried bysaid arm arranged to move said resilient members against the pull ofsaid magnet coils to open the circuit therethrough, whereby the controlis turned over to said high speed receiver.

- In witness whereof, we have hereunto set our hands this 21st day ofApril, 1925.

EDWARD M. HEWLETT. WALDO W. WILLARD.

